Optical power measurement in a passive optical network

ABSTRACT

A device and method for optical power measurement in an optical network supporting upstream and downstream signal propagation along an optical transmission path. The device includes an upstream wavelength analyzer receiving upstream light extracted from the optical transmission path and configured to determine an upstream spectral characteristic of the extracted upstream light. The device also includes a downstream filter assembly receiving downstream light extracted from the optical transmission path and configured to spectrally split the extracted downstream light into a plurality of downstream signals, one of which corresponding to a downstream signal of interest. The device further includes a processing unit configured to identify, based on the upstream spectral characteristic, the downstream signal of interest among the downstream filtered signals, and a downstream optical power meter assembly coupled to the downstream filter assembly and configured to measure an optical power parameter of the downstream signal of interest.

This patent application is a continuation-in-part of U.S. patentapplication Ser. No. 15/263,986 filed Sep. 13, 2016, now pending, whichclaims priority to U.S. Provisional Patent Application Ser. Nos.62/221,678, filed Sep. 22, 2015, and 62/288,199, filed Jan. 28, 2016.The entirety of each of these related patent applications isincorporated by reference herein.

TECHNICAL FIELD

The technical field generally relates to passive optical networks(PONs), and more particularly, to a device and method for optical powermeasurement in a PON.

BACKGROUND

Optical fiber networks lie at the core of modern telecommunications. Asthe cost of optical fibers and associated components decreases, networkarchitectures increasingly use optical fibers from the edge of a corenetwork to a location at or very close to the end users. Suchimplementations are referred to as “fiber to the X” (FTTX), where X canstand for the home (FTTH), office (FTTO), building (FTTB), curb (FTTC),premises (FTTP), etc. For cost considerations, FTTX solutions aregenerally deployed with passive optical network (PON) architectures inwhich data, voice, video and other services are conveyed to the endusers through passive splitting, rather than active switching, devices.

A PON generally consists of one or more optical line terminals (OLTs),typically located in a service provider's central office, a number ofoptical network terminals (ONTs) or units (ONUs), typically located nearthe end users, and an optical distribution network (ODN) includingoptical fibers to connect the OLTs to the ONTs and supplemented withpower and wavelength splitters, filters and other passive opticaldevices. Many PON protocols have been developed by standard bodies suchas the International Telecommunication Union (ITU) and the Institute ofElectrical and Electronics Engineers (IEEE). Non-limiting examples ofPON protocols include: asynchronous transfer mode PON (APON); broadbandPON (BPON); gigabit-capable PON (GPON); Ethernet PON (EPON);10-gigabit-capable PON (10G-PON or XG-PON); and next-generation PON 2(NG-PON2). It is to be noted that for simplicity, the term “ABG-PON”will be used herein to encompass APON, BPON, GPON and otherolder-generation “legacy” PONs that use the 1490 nanometer (nm)wavelength for downstream traffic and the 1310 nm wavelength forupstream traffic.

PONs involve bidirectional single-fiber communication between pairs ofnetwork elements, in which one network element in each pair isconfigured to interrupt signal transmission if the optical link betweenthe two network elements is broken. Because of this, optical powermeasurement of PON signals is generally performed with special-purposeor dedicated power meter instruments. These instruments are configuredto ensure that transmission of one of the communication signals ismaintained while attempting to measure the optical power of the other,counterpropagating signal.

FIG. 1 illustrates an example of a conventional PON power meter (PPM)design suitable for legacy PONs. Other implementations of such a PPMdesign are described, for instance, in U.S. Pat. Nos. 7,187,861;7,995,915; 8,861,953; and 9,287,974, the disclosures of which areincorporated herein by reference in their entirety. However, while thePPM design shown in FIG. 1 can be advantageous in many applications, itis generally unable to distinguish among multiple downstream OLT signalspropagating in different data-carrying wavelength-division-multiplexing(WDM) channels (aside from a possible signal centered near 1550 nm, forexample a CATV signal, which can be selected with a bandpass opticalfilter). This PPM design is also generally unable to identify theparticular downstream WDM or dense WDM (DWDM) wavelength associated withthe ONT for which power measurements are performed.

In NG-PON2, the optical transmission path between an OLT and an ONT maycarry multiple downstream optical signals in respective WDM channels.However, the number of these downstream signals propagating in a givenoptical transmission is, in general, not known precisely. Also, despitethe presence of multiple downstream WDM channels, generally only asingle one of these channels is actually read or listened to by the ONT,the wavelength of which being generally unknown or not readilyaccessible to the PPM and/or the operator tasked to troubleshoot orassess conformity of the communication link between the OLT and the ONT.In such a case, conventional legacy PPMs are limited to measuring onlythe total optical power carried by all of the downstream optical signalsforming the downstream light, which is generally insufficient to confirmwhether the WDM channel actually read by the ONT is present, let aloneto indicate its optical power.

Furthermore, PPM designs such as shown in FIG. 1 are generally not welladapted for optical power measurement in next-generation,multiple-wavelength PON systems, such as NG-PON2, involving both timeand wavelength division multiplexing (TWDM) in both the downstream andupstream directions. The NG-PON2 architecture is specified in the ITU-TG.989 family of recommendations, including ITU-T G.989.1 and G.989.2.For example, the ITU-T G.989.2 recommendation specifies differentoperation modes for NG-PON2, including a TWDM PON operation mode, inwhich each ONT may communicate with multiple OLTs, and a point-to-point(PtP) WDM PON operation mode. For some applications, a PPM suitable forNG-PON2 networks may need to accommodate both of these two operationmodes.

NG-PON2 is also backward-compatible with legacy PON architectures suchas GPON and XG-PON, RF video overlay, and optical time-domainreflectometer (OTDR) measurements (see, e.g., the ITU-T G989.2recommendation for NG-PON2, as well as the ITU-T G.984 and ITU-T G.987families of recommendations for GPON and XG-PON, respectively). Inparticular, different legacy PON architectures and different NG-PON2architectures can coexist on a given PON. In this context, it would beinconvenient, time-consuming and/or error-prone to require the operatorto reconfigure a PPM before each measurement in accordance with theparticular PON architecture at the OLT currently being tested.

Accordingly, various challenges remain in the development of PPMs thatcan allow optical power measurement of communication signals inmultiple-wavelength PON systems.

SUMMARY

According to an aspect, there is provided a device for optical powermeasurement in an optical network supporting upstream and downstreamsignal propagation along an optical transmission path. The deviceincludes:

-   -   an upstream wavelength analyzer receiving upstream light        extracted from the optical transmission path and configured to        determine an upstream spectral characteristic of the extracted        upstream light;    -   a downstream filter assembly receiving downstream light        extracted from the optical transmission path and configured to        spectrally split the extracted downstream light into a plurality        of downstream filtered signals, one of which corresponding to a        downstream signal of interest;    -   a processing unit configured to identify, based on the upstream        spectral characteristic, the downstream signal of interest among        the plurality of downstream filtered signals; and    -   a downstream optical power meter assembly coupled to the        downstream filter assembly and configured to measure an optical        power parameter of the downstream signal of interest.

In some implementations, the upstream wavelength analyzer is configuredto output the upstream spectral characteristic as a detection signalcorresponding to a wavelength value of the extracted upstream light.

In some implementations, the upstream wavelength analyzer is configuredto output the upstream spectral characteristic as a detection signalconveying information about a presence of the extracted upstream lightin a specific upstream spectral range.

In some implementations, the specific upstream spectral rangecorresponds to one among a first upstream spectral band ranging fromabout 1260 nm to 1280 nm, a second upstream spectral band ranging fromabout 1290 nm to about 1330 nm, and a third upstream spectral bandranging from about 1524 nm to about 1544 nm.

In some implementations, the processing unit is configured to identifythe downstream signal of interest among the plurality of downstreamfiltered signals by determining an expected value of a spectral positionof the downstream signal of interest.

In some implementations, the processing unit is configured to identifythe downstream signal of interest among the plurality of downstreamfiltered signals by determining an expected downstream spectral range inwhich to find the downstream signal of interest.

In some implementations, the expected downstream spectral rangecorresponds to one among a first downstream spectral band ranging atleast from 1575 nm to about 1580 nm, a second downstream spectral bandranging from about 1480 nm to about 1500 nm, a third downstream spectralband ranging from about 1550 nm to about 1560 nm, and a fourthdownstream spectral band ranging from about 1596 nm to about 1603 nm.

In some implementations, the optical network supports coexistence of atleast a first network standard and a second network standard, the firstand second network standards having spectrally distinct first and secondupstream transmission bands, and the upstream wavelength analyzerincludes:

an upstream optical power splitter assembly configured to split theextracted upstream light into a first upstream light component and asecond upstream light component;

an upstream filter assembly configured to filter, as a filtered upstreamsignal, the second upstream light component in a passband containingonly one of the first and second upstream transmission bands; and

an upstream detection assembly configured to measure a first opticalpower parameter of the first upstream light component and a secondupstream optical power parameter of the filtered upstream signal, theupstream detection assembly generating a detection signal based on thefirst and second optical power parameters, the detection signal beingindicative of the upstream spectral characteristic and conveyinginformation about a presence of the upstream light in one of the firstand second upstream transmission bands.

In some implementations, the first upstream transmission band rangesfrom about 1524 nm to about 1544 nm and the second upstream transmissionband ranges from about 1290 nm to about 1330 nm.

In some implementations, when the extracted upstream light is found tobe present in the first upstream transmission band, the processing unitdetermines that the downstream signal of interest lies in a firstdownstream transmission band ranging from about 1596 nm to about 1603nm; and, when the extracted upstream light is found to be present in thesecond upstream transmission band, the processing unit determines thatthe downstream signal of interest lies in a second downstreamtransmission band ranging from about 1480 nm to about 1500 nm.

In some implementations, the first upstream transmission band rangesfrom about 1260 nm to about 1280 nm and the second upstream transmissionband ranges from about 1290 nm to about 1330 nm.

In some implementations, when the extracted upstream light is found tobe present in the first upstream transmission band, the processing unitdetermines that the downstream signal of interest lies in a firstdownstream transmission band ranging from about 1575 nm to about 1580nm; and, when the extracted upstream light is found to be present in thesecond upstream transmission band, the processing unit determines thatthe downstream signal of interest lies in a second downstreamtransmission band ranging from about 1480 nm to about 1500 nm.

In some implementations, the optical network supports coexistence of atleast a first network standard and a second network standard, the firstnetwork standard having a first upstream transmission band ranging fromabout 1524 nm to about 1544 nm and the second network standard having asecond upstream transmission band ranging from about 1290 nm to about1330 nm. When the extracted upstream light is found to be present in thefirst upstream transmission band, the processing unit determines thatthe downstream signal of interest lies in a first downstreamtransmission band ranging from about 1596 nm to about 1603 nm, and whenthe extracted upstream light is found to be present in the secondupstream transmission band, the processing unit determines that thedownstream signal of interest lies in a second downstream transmissionband ranging from about 1480 nm to about 1500 nm.

According to another aspect, there is provided a method for opticalpower measurement in an optical network supporting upstream anddownstream signal propagation along an optical transmission path. Themethod includes:

-   -   receiving upstream light extracted from the optical transmission        path;    -   determining an upstream spectral characteristic of the extracted        upstream light;    -   receiving downstream light extracted from the optical        transmission path;    -   spectrally splitting the extracted downstream light into a        plurality of downstream filtered signals, one of which        corresponding to a downstream signal of interest;    -   identifying, based on the upstream spectral characteristic, the        downstream signal of interest among the plurality of downstream        filtered signals; and    -   measuring an optical power parameter of the downstream signal of        interest.

In some implementations, determining the upstream spectralcharacteristic includes generating a detection signal corresponding to awavelength value of the extracted upstream light.

In some implementations, determining the upstream spectralcharacteristic includes generating a detection signal conveyinginformation about a presence of the extracted upstream light in aspecific upstream spectral range.

In some implementations, identifying the downstream signal of interestamong the plurality of downstream filtered signals includes determiningan expected value of a spectral position of the downstream signal ofinterest.

In some implementations, identifying the downstream signal of interestamong the plurality of downstream filtered signals includes determiningan expected downstream spectral range in which to find the downstreamsignal of interest.

In some implementations, the optical network supports coexistence of atleast a first network standard and a second network standard, the firstand second network standards having spectrally distinct first and secondupstream transmission bands. In such implementations the method furtherincludes:

splitting the extracted upstream light into a first upstream lightcomponent and a second upstream light component;

filtering, as a filtered upstream signal, the second upstream lightcomponent in a passband containing only one of the first and secondupstream transmission bands;

measuring a first optical power parameter of the first upstream lightcomponent and a second upstream optical power parameter of the filteredupstream signal; and

generating a detection signal based on the first and second opticalpower parameters, the detection signal being indicative of the upstreamspectral characteristic and conveying information about a presence ofthe upstream light in one of the first and second upstream transmissionbands.

In some implementations, the first upstream transmission band rangesfrom about 1524 nm to about 1544 nm, and the second upstreamtransmission band ranges from about 1290 nm to about 1330 nm. In suchimplementations, the method further includes: determining that thedownstream signal of interest lies in a first downstream transmissionband ranging from about 1596 nm to about 1603 nm when the extractedupstream light is found to be present in the first upstream transmissionband; and determining that the downstream signal of interest lies in asecond downstream transmission band ranging from about 1480 nm to about1500 nm when the extracted upstream light is found to be present in thesecond upstream transmission band.

In some implementations, the first upstream transmission band rangesfrom about 1260 nm to about 1280 nm, and the second upstreamtransmission band ranges from about 1290 nm to about 1330 nm. In suchimplementations, the method further includes: determining that thedownstream signal of interest lies in a first downstream transmissionband ranging from about 1575 nm to about 1580 nm when the extractedupstream light is found to be present in the first upstream transmissionband; and determining that the downstream signal of interest lies in asecond downstream transmission band ranging from about 1480 nm to about1500 nm when the extracted upstream light is found to be present in thesecond upstream transmission band.

In some implementations, the optical network supports coexistence of atleast a first network standard and a second network standard, the firstnetwork standard having a first upstream transmission band ranging fromabout 1524 nm to about 1544 nm and the second network standard having asecond upstream transmission band ranging from about 1290 nm to about1330 nm. In such implementations, the method further includes:determining that the downstream signal of interest lies in a firstdownstream transmission band ranging from about 1596 nm to about 1603 nmwhen the extracted upstream light is found to be present in the firstupstream transmission band; and determining that the downstream signalof interest lies in a second downstream transmission band ranging fromabout 1480 nm to about 1500 nm when the extracted upstream light isfound to be present in the second upstream transmission band.

According to another aspect, there is provided a device for opticalpower measurement along an optical transmission path between a firstnetwork element and a second network element, the optical transmissionpath supporting bidirectional propagation of downstream light andupstream light, the downstream light including a plurality of downstreamsignals having mutually different central wavelengths. The deviceincludes:

-   -   an optical power splitter assembly configured to extract, from        the optical transmission path, a portion of the downstream light        and a portion of the upstream light;    -   an upstream wavelength analyzer configured to receive the        extracted portion of the upstream light and determine therefrom        an upstream spectral characteristic of the upstream light;    -   a processing unit coupled to the upstream wavelength analyzer        and configured to determine, based on the upstream spectral        characteristic, a downstream spectral characteristic of a        downstream signal of interest among the plurality of downstream        signals;    -   a downstream filter assembly configured to receive and filter        the extracted portion of the downstream light to select        therefrom a portion of the downstream signal of interest        according to the determined downstream spectral characteristic;        and    -   a downstream optical power meter assembly configured to measure        an optical power parameter of the portion of the downstream        signal of interest selected by the downstream filter assembly.

In some implementations, the upstream wavelength analyzer is configuredto determine the upstream spectral characteristic as a value of acentral wavelength of the upstream light, and the processing unit isconfigured to determine the downstream spectral characteristic as avalue of a central wavelength of the downstream signal of interest.

In some implementations, the processing unit is configured to determinethe value of the central wavelength of the downstream signal of interestfrom reference data relating a set of possible central wavelength valuesfor the upstream light to a set of possible central wavelength valuesfor the downstream signal of interest.

In some implementations, the downstream filter assembly has a passbandcentral wavelength tunable to the determined value of the centralwavelength of the downstream signal of interest.

In some implementations, the tunable passband central wavelength istunable in a wavelength range extending at least from 1524 nm to 1625nm.

In some implementations, the tunable passband central wavelength istunable in a wavelength range extending at least from 1596 nm to 1603nm.

In some implementations, the upstream wavelength analyzer is configuredto monitor a presence of the upstream light in each of a plurality ofdistinct upstream spectral bands and, upon detection of the presence ofthe upstream light in one of the plurality of distinct upstream spectralbands, to generate a detection signal indicative of the upstreamspectral characteristic.

In some implementations, the plurality of distinct upstream spectralbands includes a first upstream spectral band ranging at least from 1260nm to 1280 nm, a second upstream spectral band ranging at least from1290 nm to 1330 nm, and a third upstream spectral band ranging at leastfrom 1524 nm to 1625 nm.

In some implementations, the detection signal provides a value of acentral wavelength of the upstream light.

In some implementations, the detection signal is indicative of a valueof a central wavelength of the upstream light, the downstream filterassembly has a tunable passband central wavelength, and the processingunit is configured to determine a value of a central wavelength of thedownstream signal of interest based on the value of the centralwavelength of the upstream light, the tunable passband centralwavelength of the downstream filter assembly being tuned to thedetermined value of the central wavelength of the downstream signal ofinterest.

In some implementations, the upstream wavelength analyzer includes:

-   -   an upstream filter assembly configured to filter the extracted        portion of the upstream light according to a plurality of        passbands corresponding to the plurality of distinct upstream        spectral bands; and    -   an upstream detection assembly including a plurality of upstream        detection circuits, each detection circuit being configured to        receive a filtered signal from the upstream filter assembly in a        respective one of the plurality of passbands and to generate the        detection signal indicative of the upstream spectral        characteristic upon detection of the presence of the upstream        light in the respective one of the plurality of passbands.

In some implementations, at least one of the plurality of upstreamdetection circuits is configured to generate, as the detection signal, asignal representative of the presence of the filtered signal from theupstream filter assembly in the respective passband, while the remainderof the plurality of upstream detection circuits is configured togenerate, as the detection signal, a central wavelength of the filteredsignal received from the associated optical filter.

In some implementations of the device:

-   -   the downstream filter assembly is configured to spectrally split        the extracted portion of the downstream light according to a        plurality of downstream spectral bands; and    -   the downstream optical power meter assembly includes a plurality        of power meter devices, each power meter device being configured        to measure an optical power parameter of a filtered signal        received from the downstream filter assembly in a corresponding        one of the downstream spectral bands, one of the optical power        parameters measured by the power meter devices corresponding to        the optical power parameter of the portion of the downstream        signal of interest.

In some implementations, the processing unit is configured to identify,based on the determined downstream spectral characteristic, the opticalpower parameter corresponding to the optical power parameter of theportion of the downstream signal of interest.

In some implementations of the device:

-   -   the downstream signal of interest and the downstream spectral        characteristic are respectively a first downstream signal of        interest and a first downstream spectral characteristic;    -   the processing unit is configured to determine, based on the        upstream spectral characteristic, an additional downstream        spectral characteristic of an additional downstream signal of        interest among the plurality of downstream signals, the first        and the additional downstream signals of interest lying in        different ones of the downstream spectral bands; and    -   the optical power parameter measured by another one of the power        meter devices corresponds to an optical power parameter of a        portion of the additional downstream signal of interest.

In some implementations, the plurality of downstream spectral bandsincludes a first downstream spectral band ranging at least from 1575 nmto 1580 nm, a second downstream spectral band ranging at least from 1480nm to 1500 nm, a third downstream spectral band ranging at least from1550 nm to 1560 nm, and a fourth downstream spectral band ranging atleast from 1596 nm to 1603 nm.

In some implementations, the device includes first and second connectorports connected to the optical power splitter assembly for seriallyinserting the device in the optical transmission path between the firstand the second network elements.

In some implementations, the upstream wavelength is configured tomeasure an optical power parameter and/or an upstream transmissionbitrate associated with the upstream light.

According to another aspect, there is provided a device for opticalpower measurement along an optical transmission path between a firstnetwork element and a second network element, the optical transmissionpath supporting bidirectional propagation of downstream light andupstream light, the downstream light including a plurality of downstreamsignals having mutually different central wavelengths. The deviceincludes:

-   -   an optical power splitter assembly configured to extract, from        the optical transmission path, a portion of the downstream light        and a portion of the upstream light;    -   an upstream wavelength analyzer configured to receive the        extracted portion of the upstream light from the optical power        splitter assembly and to measure therefrom a value of a central        wavelength of the upstream light;    -   a downstream filter assembly configured to receive and filter        the extracted portion of the downstream light to select        therefrom a portion of the downstream signal of interest, the        downstream filter assembly having a tunable passband central        wavelength;    -   a processing unit coupled to the upstream wavelength analyzer        and the downstream filter assembly, the processing unit being        configured to determine, from the measured value of the central        wavelength of the upstream light, a value of a central        wavelength of a downstream signal of interest among the        plurality of downstream signals, the tunable passband central        wavelength of the downstream filter assembly being tuned to the        determined value of the central wavelength of the downstream        signal of interest, thereby selecting the portion of the        downstream signal of interest; and    -   a downstream optical power meter assembly configured to measure        an optical power parameter of the portion of the downstream        signal of interest selected by the downstream filter assembly.

In some implementations, the tunable passband central wavelength of thedownstream filter assembly is tunable in a wavelength range extending atleast from 1524 nm to 1625 nm.

In some implementations, the tunable passband central wavelength of thedownstream filter assembly is tunable in a wavelength range extending atleast from 1596 nm to 1603 nm.

According to another aspect, there is provided a method for opticalpower measurement along an optical transmission path between a firstnetwork element and a second network element, the optical transmissionpath supporting bidirectional propagation of downstream light andupstream light, the downstream light including a plurality of downstreamsignals having mutually different central wavelengths. The methodincludes:

-   -   extracting, from the optical transmission path, a portion of the        downstream light and a portion of the upstream light;    -   determining, from the extracted portion of the upstream light,        an upstream spectral characteristic of the upstream light;    -   determining, based on the upstream spectral characteristic, a        downstream spectral characteristic of a downstream signal of        interest among the plurality of downstream signals;    -   filtering the extracted portion of the downstream light to        select therefrom a portion of the downstream signal of interest        according to the determined downstream spectral characteristic;        and    -   measuring an optical power parameter of the selected portion of        the downstream signal of interest.

In some implementations, determining the upstream spectralcharacteristic includes measuring a value of a central wavelength of theupstream light, and determining the downstream spectral characteristicincludes determining a value of a central wavelength of the downstreamsignal of interest.

In some implementations, determining the value of the central wavelengthof the downstream signal of interest includes accessing reference datarelating a set of possible central wavelength values for the upstreamlight to a set of possible central wavelength values for the downstreamsignal of interest.

In some implementations, filtering the extracted portion of thedownstream light includes tuning a passband center wavelength to thedetermined value of the central wavelength of the downstream signal ofinterest.

In some implementations, tuning the passband center wavelength includestuning the passband center wavelength in a wavelength range extending atleast from 1524 nm to 1625 nm.

In some implementations, tuning the passband center wavelength includestuning the passband center wavelength in a wavelength range extending atleast from 1596 nm to 1603 nm.

In some implementations, determining the upstream spectralcharacteristic includes monitoring a presence of the upstream light ineach of a plurality of distinct upstream spectral bands and, upondetection of the presence of the upstream light in one of the upstreamspectral bands, generating a detection signal indicative of the upstreamspectral characteristic.

In some implementations of the method:

-   -   filtering the extracted portion of the downstream light includes        spectrally splitting the extracted portion of the downstream        light into a plurality of downstream spectral bands; and    -   measuring the optical power parameter of the portion of the        downstream signal of interest includes measuring an optical        power parameter of a filtered signal in each of the downstream        spectral bands, one of the optical power parameters measured by        the power meter devices corresponding to the optical power        parameter of the portion of the downstream signal of interest.

In some implementations, the method further includes identifying, basedon the determined downstream spectral characteristic, the one of theoptical power parameters measured by the power meter devicescorresponding to the optical power parameter of the portion of thedownstream signal of interest.

According to another aspect, there is provided a PPM that identifies anactual mode of operation being used and auto-adapts to perform theproper measurement as a function of the identified mode. This may beperformed by identifying the wavelength or wavelength range of the ONTupstream signal(s).

According to another aspect, there is provided a device for measuringalong an optical transmission path a parameter of at least one ofoptical signals propagating concurrently in opposite directions betweena first network element and a second network element, the deviceincluding: a wavelength-meter receiving an extracted portion of lightpropagating upstream along the optical transmission path, for measuringa wavelength of an upstream optical signal; a processing unit todetermine an expected WDM channel of a downstream signal from themeasured wavelength of said upstream optical signal and preset networkconfiguration data; an optical filter receiving an extracted portion oflight propagating downstream along the optical transmission path toselect in said extracted portion of light propagating downstream, saiddownstream optical signal; and a power meter receiving the selecteddownstream optical signal to measure an optical power value associatedthereto.

In some implementations, the optical filter is tunable to the expectedWDM channel.

According to another aspect, there is provided a method for measuringalong an optical transmission path a parameter of at least one ofoptical signals propagating concurrently in opposite directions betweena first network element and a second network element, the methodincluding: measuring a wavelength of an upstream optical signal;determining an expected WDM channel of a downstream signal from themeasured wavelength of said upstream optical signal and preset networkconfiguration data; filtering an extracted portion of light propagatingdownstream along the optical transmission path to select the downstreamoptical signal; and measuring an optical power value associated with thedownstream optical signal.

In some implementations, the first network element transmits adownstream optical signal in a first WDM channel, the second networkelement transmits an upstream optical signal in a second WDM channel,and the optical transmission path may also carry other downstreamoptical signals in other WDM channels.

Other features and advantages of the techniques described herein will bebetter understood upon reading of exemplary embodiments thereof withreference to the appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 (PRIOR ART) is a schematic block diagram of a conventional PPMsuitable for optical power measurement in a legacy PON system.

FIG. 2 is a schematic block diagram of a device for optical powermeasurement in a multiple-wavelength PON system shown along withelements of the PON system, in accordance with a first exemplaryembodiment.

FIG. 3 is a schematic block diagram of a device for optical powermeasurement in a multiple-wavelength PON system shown along withelements of the PON system, in accordance with a second exemplaryembodiment.

FIG. 4 is a schematic block diagram of a device for optical powermeasurement in a multiple-wavelength PON system shown along withelements of the PON system, in accordance with a third exemplaryembodiment.

FIG. 5 is a schematic block diagram of a device for optical powermeasurement in a multiple-wavelength PON system shown along withelements of the PON system, in accordance with a fourth exemplaryembodiment.

FIG. 6 is a schematic block diagram of a device for optical powermeasurement in a multiple-wavelength PON system shown along withelements of the PON system, in accordance with a fifth exemplaryembodiment.

FIG. 7 is a flow chart of a method for optical power measurement alongan optical transmission path between two network elements, in accordancewith an exemplary embodiment.

DETAILED DESCRIPTION

In the following description, similar features in the drawings have beengiven similar reference numerals, and, to not unduly encumber thefigures, some elements may not be indicated on some figures if they werealready identified in one or more preceding figures. It should also beunderstood herein that the elements of the drawings are not necessarilydepicted to scale, since emphasis is placed upon clearly illustratingthe elements and structures of the present embodiments. Some optical,electrical and/or mechanical elements may also be omitted on some or allof the figures in order to emphasize inventive aspects of theillustrated embodiments.

The present description generally relates to a device and method foroptical power measurement along an optical transmission path between afirst network element and a second network element of an opticalnetwork.

The present techniques can be useful in applications where it isdesirable or required to provide on-site optical power measurement ofPON signals in multiple-wavelength PON networks to ensure that thenetwork is reliable and that it operates within acceptable industryspecifications. The present techniques can be field portable and beimplemented in various environments and settings, includingfield-deployed networks, manufacturing facilities for network equipment,research and development laboratories, and the like. The presenttechniques can be employed during the installation, activation and/oroperation phases of the network for the purpose of opticalcharacterization, error diagnosis and troubleshooting, and/or performingmonitoring.

As known in the art, a PON is a communication network that does notrequire active components to convey communication signals betweennetwork elements. A PON is typically composed of one or more OLTslocated at a service provider's central office or hub, a number of ONTslocated at or near respective customers' premises, and an ODN betweenthem. The OLTs and the ONTs include optical transmitters and receiversto allow simultaneous, bidirectional transmission of downstream andupstream traffic. Generally, OLTs are responsible for allocatingupstream bandwidth to the ONTs in order to prevent interference betweenupstream signals originating from different ONTs. As a result, ONTs areconfigured to transmit upstream data only if they receive OLT downstreamdata. For this reason, conventional PPM devices used in legacy PONsystems are configured to perform optical power testing whilemaintaining OLT-to-ONT communications.

As mentioned above, a limitation of these conventional PPM devices isthat they generally cannot distinguish among multiple downstream signalspropagating at different wavelengths, let alone identify the wavelengthor wavelength range of the one among the downstream signals actuallyread by the ONT being tested. This limitation can make conventional PPMdevices impractical for use in next-generation, multiple-wavelength PONsystems, such as NG-PON2. In order to try to address or at leastalleviate these issues, the present techniques aim to provide a deviceand method for optical power measurement suitable for implementation inmultiple-wavelength PON systems, including NG-PON2 systems, NG-PON2systems with coexistence of one or more legacy PON systems, and othernext-generation PON systems.

As described in greater detail below, the present techniques can involveidentifying the spectral region containing the upstream signaloriginating from the ONT under test so as to provide knowledge about thespectral region in which to find the downstream signal read by this ONT,whose optical power is to be measured. The identification of thespectral region in which the upstream signal is contained can alsoprovide information about the operation mode, or PON protocol, of theONT under test (e.g., NG-PONG2, XG-PON or ABG-PON). In particular,implementations described herein can provide “auto-discovery” or“network-aware” capabilities, with which the PPM device can configureitself based on the information about the operation mode implemented inthe ONT under test derived from the spectral analysis of its upstreamsignal.

First Embodiment of a Device for Optical Power Measurement

Referring to FIG. 2, there is illustrated a first exemplary embodimentof a device 10, which is operable as a PON power meter. As discussedbelow, the device 10 generally includes four main components, namely anoptical power splitter assembly 12, an upstream wavelength analyzer 14,a processing unit 16, a downstream filter assembly 18, and a downstreamoptical power meter assembly 20.

As shown in FIG. 2, the device 10 can be used for optical powermeasurement along an optical transmission path 22 extending between afirst network element 24 and a second network element 26 in a PON 28.The optical transmission path supports concurrent, bidirectionalpropagation of downstream light 30 and upstream light 32. In theillustrated embodiment, the first network element 24 and the secondnetwork element 26 are respectively embodied by an OLT and an ONT.

It is to be noted that throughout the present description, the terms“light” and “optical” are understood to refer to radiation in anyappropriate region of the electromagnetic spectrum. In particular, theterms “light” and “optical” are not limited to visible light, but caninclude, for example, the infrared wavelength range. For example, insome embodiments, the downstream light and the upstream light carried onthe optical transmission path may each have a wavelength lying within arange from about 1200 nm to 1700 nm, which encompasses the near-infraredtransmission window for optical telecommunication applications. Ofcourse, other wavelength ranges may be considered in other embodimentswithout departing from the scope of the present techniques.

In operation, the first and the second network elements 24, 26 are indata communication with each other. More specifically, this means that,during testing, the first network element 24 (i.e., the OLT in FIG. 2)generates a downstream signal along the optical transmission path 22.This downstream signal is received and read by the second networkelement 26 (i.e., the ONT in FIG. 2). In response, the second networkelement 26 generates an upstream signal along the optical transmissionpath 22, and this upstream signal is received and read by the firstnetwork element 24. It is to be noted that, for convenience, the firstand the second network elements 24, 26 may in some instances be referredto respectively as the “upstream” and the “downstream” network elements,hence reflecting their relative positioning in the PON 28.

In FIG. 2, the PON 28 is a multiple-wavelength PON, for exampleimplementing NG-PON2 with or without coexisting legacy PONarchitectures. By way of example, in the illustrated embodiment, the PON28 includes four OLTs, of which one corresponds to the first networkelement 24 and the others are designated by reference numeral 34.However, for simplicity, only one ONT is shown in FIG. 2, namely thesecond network element 26. Indeed, in a typical PON system, the upstreamsignal from a particular ONT is multiplexed with the upstream signalsfrom other ONTs at an optical combiner, for instance, disposed betweenthe ONTs and the OLTs, typically upstream with respect to the device 10.

In general, each OLT in a multiple-wavelength PON is operable in aparticular operation mode (e.g., NG-PONG2, XG-PON or ABG-PON) and at aparticular wavelength or wavelength range. The downstream signalsgenerated by the four OLTs can be combined with an OLT signal combiner36, for example a wavelength multiplexer. The combined OLT signals formthe downstream light 30 propagating along the optical transmission path22 toward the second network element 26. This means that the downstreamlight 30 generally includes a plurality of downstream signals havingmutually different central wavelengths.

Providing a plurality of OLTs makes it possible for each ONT in thenetwork to access downstream signals of different wavelengths orwavelength ranges although at any given time each ONT is in two-waycommunication with only one of the OLTs. Accordingly, the downstreamlight 30 propagating along the optical transmission path 22 in FIG. 2generally includes not only the downstream signal of interest 38transmitted by the first network element 24, but also other downstreamsignals 40 originating from the remaining OLTs 34. However, since onlythe downstream signal of interest 38 is actually read by the secondnetwork element 26, the other downstream signals 40 being filtered outof the downstream light 30 upon reaching the second network element 26,it is only this signal 38 which is relevant during optical powertesting. Because of this, the present description provides a techniquefor extracting the downstream signal of interest 38 from the downstreamlight 30 and measuring its optical power in order to assess networkperformance and integrity.

Referring still to FIG. 2, the device 10 can include a housing 42 toaccommodate therein various device components. In some implementations,the device 10 is portable to allow field-deployed PON testing. In such acase, the housing 42 can be ergonomically sized and shaped to facilitateholding, moving and operating of the device 10 using one or both handsof an operator. The housing 42 may be made of a lightweight yet sturdymaterial, for example molded plastic.

The housing 42 is generally provided with a first connector port 44 anda second connector port 46, for example bulkhead connector ports orother suitable types of connector ports. The first and the secondconnector ports 44, 46 are connected to the optical power splitterassembly 12 for serially inserting the device 10 in the opticaltransmission path 22 between the first and the second network elements24, 26. More specifically, inserting the device 10 in the opticaltransmission path 22 can involve disconnecting an optical fiber link 48at a testing point along the optical transmission path 22. The testingpoint can be located at an existing connectorized coupler close to thesecond network element 26, typically at the customer's premise anddownstream of any optical combiner that combines the upstream signalfrom the second element 26 with the upstream signals from other ONTs.Once the optical fiber link 48 has been disconnected, the device 10 canbe inserted into the optical transmission path 22 by connecting thefirst connector port 44 toward the upstream end of the opened link 48and the second connector port 46 toward the downstream end of the openedlink 48. In this way, the optical transmission path 22 is made to passthrough the device 10.

It is to be noted that while the optical fiber link 48 is disconnectedprior to connecting the device 10, the second network element 26 willnormally cease sending upstream data to the first network element 24.Upstream data transmission will resume once the device 10 has beenconnected to the optical transmission path and the second networkelement 26 has started receiving again downstream data from the firstnetwork element 24, at which point measurement can be performed. It isalso to be noted that the temporary disruption in the line uponinsertion of the device 10 is generally not an issue, given that thedevice 10 will often be used in diagnosis or troubleshootingapplications, where a problem with the line may have already beenreported, or under controlled verification conditions.

In some implementations, data communication between the first and thesecond network elements 24, 26 may be interrupted after a certain periodof time for the purpose of saving energy. In this state, the secondnetwork element 26 may disable its transmission circuits whilecontinuing to listen to the first network element 24, such that noupstream signal reaches the upstream wavelength analyzer 14. Gettingcommunication to resume can involve momentarily interrupting theconnection between the first and the second network elements 24, 26.Such an interruption occurs whenever the device 10 is inserted in theoptical transmission path 22 between the first and the second networkelements 24, 26. However, if communication is interrupted when thedevice 10 is already connected, disconnecting and reconnecting theinstrument will force restart of the communication. In someimplementations, in order to prevent early wear out of the first andsecond connector ports 44, 46 due to the device 10 being disconnectedand reconnected too frequently, a shutter 112 can optionally be providedinside the device 10. The shutter 112 can act as an automatic switch,configured to break and then, immediately or shortly thereafter,re-establish the continuity of the optical transmission path 22 withoutthe user having to physically disconnect the device 10. By way ofexample, the shutter may be activated by the user via a controlinterface of the device 10. The shutter 112 in FIG. 2 is provided in thepath between first connector port 44 and the optical power splitterassembly 12. However, in other implementations, the shutter 112 could beprovided at another point along the optical transmission path 22 insidethe device, for example between the optical power splitter assembly 12and the second connector port 46.

Referring still to FIG. 2, the optical power splitter assembly 12 isserially connected between the first connector port 44 and the secondconnector port 46. The optical power splitter assembly 12 is apower-dividing element configured to split the downstream light 30 andthe upstream light 32 into, on the one hand, respective extractedportions 50, 52 that branch off from the optical transmission path 22,and, on the other hand, non-extracted portions 54, 56 that remain on theoptical transmission path 22 and flow out of the device 10. In theembodiment of FIG. 2, the optical power splitter assembly 12 is embodiedby a 2×2 fiber-based bidirectional tap, but other types of opticalsplitters and couplers can be used in other embodiments.

The optical power splitter assembly 12 can include first and secondports 58 a, 58 b for respectively carrying the non-extracted portions54, 56 of the downstream light 30 and the upstream light 32 out of theoptical power splitter assembly 12 and through the device 10. Theoptical power splitter assembly 12 can also include a third port 58 cfor outputting the extracted portion 50 of the downstream light 30, anda fourth port 58 d for outputting the extracted portion 52 of theupstream light 32. It is to be noted that, for simplicity, the extractedportion of the downstream light and the extracted portion of theupstream light may in some instances be referred to as the “extracteddownstream light” and the “extracted upstream light”, respectively.

In some embodiments, the optical power splitter assembly can provide an80:20 splitting ratio. This means that the optical power splitterassembly 12 extracts 20% of the downstream light 30 and 20% of theupstream light 32 from the optical transmission path 22, with theremaining 80% flowing out of the device 10. Of course, other splittingratios may be used in other embodiments, for example a 90:10 splittingratio. Generally, a higher percentage of signal extraction improvespower measurement sensitivity, but leads to higher insertion loss forthe “pass-through” signals, which, for certain network designs, mightresult in a non-desirable reduction of system margin.

In the embodiment of FIG. 2, the upstream wavelength analyzer 14 isconfigured to receive the extracted portion 52 of the upstream light 32from the optical power splitter assembly 12, and to determine therefroman upstream spectral characteristic of the upstream light 32. Theupstream spectral characteristic can be representative of a centralwavelength of the upstream light 32.

Throughout the present description, the term “upstream wavelengthanalyzer” is intended to refer broadly to any element or combination ofelements capable of receiving, manipulating (e.g., splitting andspectrally filtering) and detecting the extracted portion of theupstream light for the purpose of determining the upstream spectralcharacteristic. As described in greater detail below, the upstreamwavelength analyzer may be configured to monitor simultaneously apresence of the upstream light in each of a plurality of distinctupstream spectral bands (e.g., a wavelength band or a frequency band)and, upon detection of the presence of the extracted portion of theupstream light in one of the upstream spectral bands, to generate adetection signal indicative of the upstream spectral characteristic.

In some implementations, the detection signal indicative of the upstreamspectral characteristic can be a signal indicative of a presence of theextracted upstream light in one of the upstream spectral bands (or in aportion thereof). By way of example, the detection signal may be abinary indication of a certain magnitude corresponding to a detectedthreshold value, or a quantified value or measurement (e.g., a measuredoptical power parameter). In other implementations, the detection signalindicative of the upstream spectral characteristic can be a measuredvalue corresponding to a wavelength (or, equivalently, a frequency)associated with the upstream light, for example a measured value of acentral wavelength (or, equivalently, a central frequency) of theupstream light. It is to be noted that, in many cases of interest, theupstream light originating from the first network element does indeedhave a relatively simple spectrum, composed of either of a single peakat a certain spectral position, or a single band in a certain spectralrange.

In the embodiment of FIG. 2, the processing unit 16 is coupled to theupstream wavelength analyzer 14. The processing unit 16 is configured toidentify, based on the upstream spectral characteristic determined bythe upstream wavelength analyzer 14, an associated downstream spectralcharacteristic of a downstream signal of interest 38 among the pluralityof downstream signals 38, 40 making up the downstream light 30. Thedownstream spectral characteristic can be representative of a centralwavelength of the downstream signal of interest 38. By way of example,in some implementations, the downstream spectral characteristic can be aspectral range (e.g., a wavelength or frequency range) in which thedownstream signal of interest 38 is expected to lie. Alternatively, inother implementations, the downstream spectral characteristic can be anexpected value of a wavelength (or, equivalently, a frequency) of thedownstream signal of interest, for example a nominal value of itscentral wavelength or, equivalently, its central frequency).

As used herein, the term “processing unit” refers to an entity of thedevice that controls and executes, at least partially, the functionsrequired to determine the downstream spectral characteristic associatedwith the upstream spectral characteristic of the upstream lightdetermined by the upstream wavelength analyzer. The processing unit maybe implemented as a single unit or as a plurality of interconnectedprocessing sub-units. The processing unit may be embodied by amicroprocessor, a microcontroller, a central processing unit (CPU), aprogrammable logic device such as, for example, a field-programmablegate array (FPGA), or any other type of processing resource or anycombination of such processing resources configured to operatecollectively as a processing unit. The processing unit can beimplemented in hardware, software, firmware, or any combination thereof,and be connected to various components of the device via appropriatecommunication ports.

Referring still to FIG. 2, the identification made by the processingunit 16 is based on the principle that the upstream spectralcharacteristic (e.g., a wavelength value or wavelength range of theupstream light) determined by the upstream wavelength analyzer 14 can beused to yield information about the downstream spectral characteristic(e.g., a corresponding wavelength value or wavelength range of thedownstream signal of interest). As mentioned above, the downstreamsignal of interest is, among the plurality of downstream signals formingthe downstream light, the downstream signal which is generated by thefirst network element (e.g., an OLT in FIG. 2) and listened to by thesecond network element (e.g., an ONT in FIG. 2). The information aboutthe spectral characteristic of the upstream light may also provideknowledge about the operation mode of the ONT being tested (e.g.,NG-PONG2, XG-PON or ABG-PON).

In some implementations, the processing unit 16 can be configured todetermine the downstream spectral characteristic associated with theupstream spectral characteristic from reference data relating a set ofpossible upstream spectral characteristics to a set of possibledownstream spectral characteristics, for example a set of possiblecentral wavelength values for the upstream light to a set of possiblecentral wavelength values for the downstream signal of interest. Thereference data can represent preset network-dependent configuration dataand standards and be embodied by a lookup table stored in a memoryelement accessible to processing unit 16. By way of example, and asdescribed in greater detail below, the processing unit 16 can use storedinformation about PON standards to determine that if the centralwavelength of the upstream light is between 1290 nm and 1330 nm, thenthe second network element should be an ABG-PON device and the centralwavelength of the downstream signal of interest should be found between1575 nm and 1580 nm.

In the embodiment of FIG. 2, the downstream filter assembly 18 isconfigured to receive and filter the extracted portion 50 of thedownstream light 30 from the optical power splitter assembly 12. Thepurpose of filtering the extracted downstream light 50 is to selecttherefrom the extracted portion 60 of the downstream signal of interest38 according to the determined downstream spectral characteristic.

In some implementations, the downstream filter assembly 18 can include anumber of spectrally selective elements (e.g., optical splitters andfilters) configured to isolate the extracted portion 60 of thedownstream signal of interest 38 from the extracted downstream light 50.By way of example, the downstream filter assembly 18 can be configuredto spectrally split the extracted downstream light 50 into a pluralityof downstream spectral bands, one of which contains the extractedportion 60 of the downstream signal of interest 38. As mentioned above,in some implementations, the processing unit 16 is configured todetermine the downstream spectral characteristic as a value of thecentral wavelength of the downstream signal of interest 38. In such acase, the downstream filter assembly 18 can include a tunable passbandcentral wavelength which the processing unit 16 is configured to tune(directly or indirectly, e.g., via a controller associated with thedownstream filter assembly) to the determined value of the centralwavelength of the downstream signal of interest 38, thereby selectingthe portion 60 of the downstream signal of interest 38.

Referring still to FIG. 2, the downstream optical power meter assembly20 is configured to measure an optical power parameter of the portion 60of the downstream signal of interest 38 selected by the downstreamfilter assembly 18. As used herein, the term “optical power parameter”is intended to encompass different parameters representative of theoptical power of the downstream signal of interest, including a peakoptical power, an average optical power measured over a given timeduration, and the like. In some implementations, the downstream opticalpower meter assembly 20 can include one or a plurality of power meterdevices. The or each power meter device can be configured to measure anoptical power parameter of a respective filtered signal outputted by thedownstream filter assembly 18 in a corresponding downstream spectralband. The or one of the optical power parameters measured by thedownstream optical power meter assembly 20 corresponds to the opticalpower parameter of the portion 60 of the downstream signal of interest38, which is relevant to the optical power measurement procedureperformed by the device 10. In some implementations where more than oneoptical power parameters are measured by the downstream optical powermeter assembly 20, the processing unit 16 can be configured to identify,based on the determined downstream spectral characteristic, which ofthese optical power parameters is the “relevant” one corresponding tothe optical power parameter of the portion 60 of the downstream signalof interest 38.

PON upstream and downstream signals typically consist of data burstsalternating with lulls. As known in the art, if the downstream signal ofinterest 38 includes a bursty digital signal, the downstream opticalpower meter assembly 20 may be configured to extract the optical powerof the bursts averaged over the duration of the burst, by extracting thepower only from the data bursts and not from any intervening series ofdigital zeros (i.e. lack of signal).

In some implementations, the results of the testing by the device 10 maybe displayed to the operator on a display 98 provided on the housing 42.By way of example, the display 98 can be embodied by a liquid crystaldisplay (LCD) screen. However, any other appropriate display technologysuch as, for example, LED technology, organic LED (OLED) technology, oractive-matrix OLED (AMOLED) technology could be used in otherembodiments. By way of example, the information presented on the displaycan include, without being limited to: the type of PON being tested(e.g., ABG-PON, XG-PON, NG-PON2, etc.), the downstream and/or upstreamtransmission rates, the downstream and/or upstream wavelengths orwavelength channels, the optical power of the downstream and/or upstreamsignals, and a pass/fail indicator.

More details regarding various other structural and operational featuresof the device and method will now be given below, with reference to theexemplary embodiments of FIGS. 3 to 5.

Second Embodiment of a Device for Optical Power Measurement

Referring now to FIG. 3, there is illustrated a second exemplaryembodiment of a device 10 operable as a PON power meter. The device 10is suitable for optical power measurement along an optical transmissionpath 22 extending between a first network element 24 and a secondnetwork element 26 in a multiple-wavelength PON 28 implementing NG-PON2with coexistence of ABG-PON, XG-PON and RF video overlay on the sameODN. In the illustrated embodiment, the first network element 24 isembodied by an OLT and the second network element 26 is embodied by anONT. The optical transmission path 22 supports concurrent, bidirectionalpropagation of downstream light 30 and upstream light 32. The downstreamlight 30 includes a plurality of downstream signals 38, 40 havingmutually different central wavelengths, one of which corresponding tothe downstream signal of interest 38, that is, the downstream signalread by the second network element 26. The device 10 aims to measure theoptical power of the downstream signal of interest 38.

Many features of this second embodiment of the device 10 can begenerally similar to like features described for the first embodiment.Accordingly, the second embodiment of the device 10 generally includesan optical power splitter assembly 12, an upstream wavelength analyzer14, a processing unit 16, a downstream filter assembly 18, and adownstream optical power meter assembly 20.

The optical power splitter assembly 12 in FIG. 3 is serially connectedbetween the first connector port 44 and the second connector port 46,and is configured to extract, from the optical transmission path 22, aportion 50 of the downstream light 30 and a portion 52 of the upstreamlight 32. As for the embodiment of FIG. 2, the optical power splitterassembly 12 in FIG. 3 is embodied by a 2×2 bidirectional tap with an80:20 splitting ratio, but other optical splitter types and splittingratio values can be used in other embodiments. The optical powersplitter assembly 12 includes four ports 58 a to 58 d. The first and thesecond ports 58 a, 58 b are used to output the non-extracted downstreamlight 54 and the non-extracted upstream light 56 that flow through thedevice, respectively. Meanwhile, the third and the fourth ports 58 c, 58d are used to output the extracted downstream light 50 and the extractedupstream light 52 along respective downstream and upstream paths 62, 64.

The upstream wavelength analyzer 14 is positioned in the upstream path64 and configured to receive the extracted upstream light 52 anddetermine therefrom an upstream spectral characteristic representativeof a central wavelength of the upstream light 32.

In the NG-PON2 standard, but also in legacy PON standards, the upstreamlight originating from a given ONT generally includes a single upstreamwavelength channel characterized by a single central wavelength.Measuring the value of the central wavelength of the upstream light ordetermining its presence in a certain upstream spectral band can provideknowledge about the downstream spectral characteristic, for example thevalue of the central wavelength of the downstream signal of interest orits presence in a corresponding downstream spectral band, as well asabout the PON standard used by the second network element.

In the embodiment of FIG. 3, the upstream wavelength analyzer 14includes an upstream filter assembly 66 configured to filter theextracted upstream light 52 and including a plurality of optical filters68 a to 68 c, each of which having a passband corresponding to one of aplurality of distinct upstream spectral bands. In some implementations,the upstream filter assembly 66 can be embodied by a demultiplexingassembly configured to demultiplex the extracted upstream light 52 intothe plurality of upstream spectral bands. By way of example, thedemultiplexing assembly may include two cascaded wavelengthdemultiplexers based, for instance, on wavelength-dependent fusedcouplers or bulk filters. Of course, other embodiments may use differentconfigurations for the upstream filter assembly 66.

In the illustrated embodiment, the upstream wavelength analyzer 14 alsoincludes an upstream detection assembly 70 configured to detect thefiltered output from the upstream filter assembly 66. The upstreamdetection assembly 70 includes a plurality of upstream detectioncircuits 72 a to 72 c respectively associated with the plurality ofoptical filters 68 a to 68 c. Each upstream detection circuit 72 a to 72c is configured to receive a filtered signal from the associated opticalfilter 68 a to 68 c and to generate, upon detection of the presence ofthe upstream light 32 in the one of the upstream spectral bands, adetection signal indicative of the upstream spectral characteristic.

The upstream detection assembly 70 is coupled to the processing unit 16.The processing unit 16 is configured to receive the detection signalindicative of the upstream spectral characteristic and to determinetherefrom a downstream spectral characteristic of the downstream signalof interest among the plurality of downstream signals forming thedownstream light 30. As mentioned above, the processing unit 16 candetermine the downstream spectral characteristic from networkconfiguration data relating a set of possible upstream spectralcharacteristics to a set of possible downstream spectralcharacteristics.

In the exemplary embodiment of FIG. 3, the upstream filter assembly 66includes three bandpass optical filters 68 a to 68 c respectivelyassociated to the three upstream detection circuits 72 a to 72 c of theupstream detection assembly 70. The three optical filters 68 a to 68 care configured to allow passage of light in three respective upstreamspectral bands, including a first upstream spectral band ranging from1260 nm to 1280 nm, a second upstream spectral band ranging from 1290 nmto 1330 nm, and a third upstream spectral band ranging from 1524 nm to1625 nm. Of course, the number and the passband spectral ranges of thebandpass optical filters 68 a to 68 c illustrated in FIG. 3 are providedby way of example only and may be varied in other embodiments.

More specifically, the first optical filter 68 a is configured to selectwavelengths in the first upstream spectral band, which ranges from 1260nm to 1280 nm (i.e., 1260 nm<λ<1280 nm). Accordingly, the extractedupstream light 52 in the first upstream spectral band passes through thefirst optical filter 68 a and reaches the first upstream detectioncircuit 72 a, which detects its presence and measures its optical power.The presence of light in the first upstream spectral band signifies thatthe second network element 26 is an XG-PON device. In such a case, theprocessing unit 16 draws a conclusion that the downstream signal ofinterest is to be found in a downstream spectral band ranging from 1575nm to 1580 nm.

By way of example, in the embodiment of FIG. 3, the first upstreamdetection circuit 72 a includes an optical-to-electrical (O/E) converter74 (e.g., an InGaAs detector) for generating an electronic signalrepresentative of the detected light, a transimpedance amplifier 76 foramplifying the electronic signal, a peak detector 78 for detecting apeak value in the amplified electronic signal, and an analog-to-digital(A/D) converter (ADC) 80 for converting the output of the peak detector78 into digital output data. The digital output data is processed toyield a value that determines the optical power of the extractedupstream light 52 in the first upstream spectral band.

Referring still to FIG. 3, the second optical filter 68 b is configuredto select wavelengths in the second upstream spectral band, which rangesfrom 1290 nm to 1330 nm (i.e., 1290 nm<λ<1330 nm). Accordingly, theextracted upstream light 52 in the second upstream spectral band passesthrough the second optical filter 68 b and reaches the second upstreamdetection circuit 72 b. The second upstream detection circuit 72 bdetects the presence of light outputted by the second optical filter 68b and measures its optical power as well as the duration of itskeep-alive burst response.

The presence of light (i.e., typically several wavelengths) in thesecond upstream spectral band is an indication that the second networkelement 26 is an ABG-PON device. In such a case, the processing unit 16concludes that a data downstream signal of interest is to be found in adownstream spectral band ranging from 1480 nm to 1500 nm. The processingunit also concludes that a video downstream signal of interest maypossibly be found in a downstream spectral band ranging from 1550 nm to1560 nm, and that an extra data downstream signal of interest maypossibly be found in a downstream spectral band ranging from 1539 nm to1565 nm (not shown in FIG. 3). The processing unit 16 may also determinethe upstream transmission bitrate from the keep-alive burst responseduration, for example based on reference data (e.g., a lookup table).

By way of example, in the embodiment of FIG. 3, the second upstreamdetection circuit 72 b includes an O/E converter 74 (e.g., an InGaAsdetector) for generating an electronic signal representative of thedetected light, and a transimpedance amplifier 76 for amplifying theelectronic signal. The amplified electronic signal is directed to apeak-and-duration detector 82, where it is split in two parts. The firstpart is directed to a peak detector. The second part is directed to afilter having a time constant longer than the longest upstream burst tobe detected by the device 10, and then to a peak detector to retrievethe average power of the upstream burst over the time corresponding tothe longest burst duration possibly supported by the device 10. An ADC80 converts the output of the peak-and-duration detector 82 into digitaloutput data. The digital output data is processed to yield two powervalues. The first power value determines the optical power of theextracted upstream light 52 in the second upstream spectral band, whilethe ratio of first power value to the second filtered power valuedetermines the upstream burst duration and, in turn, the upstream signalbitrate.

The third optical filter 68 c is configured to select wavelengths in thethird upstream spectral band, which ranges from 1524 nm to 1625 nm(i.e., 1524 nm<λ<1625 nm). Accordingly, the extracted upstream light 52in the third upstream spectral band passes through the third opticalfilter 68 c and reaches the third upstream detection circuit 72 c. Thethird upstream detection circuit 72 c detects the presence of lightoutputted by the third optical filter 68 c and measures its opticalpower, its central wavelength, and the duration of its keep-alive burstresponse.

The presence of light (i.e., a single wavelength) in the third upstreamspectral band is an indication that the second network element 26 is aNG-PON2 device implementing either a TWDM or a PtP operation mode. Insuch a case, the processing unit 16 is configured to determine theexpected value of the central wavelength of the downstream signal ofinterest from the measured value of the central wavelength of theupstream light 32 based on reference data (e.g., a lookup table)relating a set of possible central wavelength values for the upstreamlight to a set of possible central wavelength values for the downstreamsignal of interest. The processing unit 16 may also determine theupstream transmission bitrate from the keep-alive burst response. It isto be noted that since only one upstream wavelength channel is expectedto be present in the third upstream spectral range, a single-wavelengthmeter could be used in some implementations, which can reduce the costof the device. It is also to be noted that, in some implementations, thevalue of the measured upstream central wavelength may further be used tocalibrate the device 10.

Referring still to FIG. 3, the third upstream detection circuit 72 c isconfigured to measure the central wavelength and the optical power ofthe upstream light 32. The third upstream detection circuit 72 cincludes a bandpass splitting filter 84 that splits and filters incominglight from the upstream filter assembly 66 into a first signal (signalA) and a second signal (signal B) with a known or precalibratedwavelength-dependent splitting ratio in a passband ranging from 1524 nmto 1625 nm. The bandpass splitting filter 84 may be embodied by a slopefilter with the desired or required passband.

The third upstream detection circuit 72 c also includes O/E converters74 (e.g., InGaAs detectors) for generating electronic signalsrepresentative of signals A and B, and transimpedance amplifiers 76 foramplifying the two electronic signals. Each amplified electronic signalis sent to a respective peak-and-duration detector 82, where it is splitin two parts. Each first part is directed to a peak detector (P1A, P1B).Each second part is directed to a filter having a time constant longerthan the longest upstream burst to be detected by the device 10, andthen to a peak detector (P2A, P2B). An ADC 80 then converts the outputof the two peak-and-duration detectors 82 into digital output data.

The digital output data is processed to yield four power values. The sumof the power values corresponding to the two first parts (P1A+P1B)determines the optical power of the extracted upstream light 52 in thethird upstream spectral band, and the ratio of the power valuescorresponding to the two second parts (P2A/P2B) is used to determine thecentral wavelength of the extracted upstream light 52 (and thus of theupstream light 32 itself), for example using a prerecorded calibrationtable. Also, the ratio of the sum of the power values corresponding tothe two first parts to the sum of the power values corresponding to thetwo second parts [i.e., (P1A+P1B)/(P2A+P2B)] can be used to determinethe upstream burst duration and, in turn, the upstream signal bitrate.

It is to be noted that the configurations for the plurality of upstreamdetection circuits 72 a to 72 c depicted in FIG. 3 are provided by wayof example only, and may be varied in other implementations. Forexample, in some implementations, the first upstream detection circuit72 a may include a peak-and-duration detector instead of only a peakdetector, whereas each of the second and third upstream detectioncircuits 72 b, 72 c may include only a peak detector instead of apeak-and-duration detector.

Referring still to FIG. 3, the downstream filter assembly 18 ispositioned in the downstream path 62 and configured to receive andfilter the extracted portion 50 of the downstream light 30 to selecttherefrom a portion of the downstream signal of interest according tothe determined downstream spectral characteristic.

In the illustrated embodiment, the downstream filter assembly 18 iscapable of analyzing two downstream wavelength mappings, namely a firstwavelength mapping for TWDM NG-PON2, ABG-PON, XG-PON and RF videooverlay, and a second wavelength mapping for PtP NG-PON2. Two wavelengthmappings, each leading to its own detection path in the downstreamoptical power meter assembly 20 (see below), are provided in FIG. 3 toaccount for the fact that the expanded downstream spectrum for PtPNG-PON2 overlaps the downstream spectral bands of XG-PON and RF videooverlay. For this purpose, the downstream filter assembly 18 includes adownstream optical power splitter assembly 86 configured to receive theextracted downstream light 50 from the optical power splitting assembly12. The downstream optical power splitter assembly 86 is apower-dividing coupling element configured to split the extracteddownstream light 50 into a first portion 88 a and a second portion 88 b.In the embodiment of FIG. 3, downstream optical power splitter assembly86 has a 50:50 splitting ratio, but other splitting ratio values can beused in other embodiments (e.g., 40:60). The first extracted downstreamlight portion 88 a is used to detect TWDM NG-PON2, ABG-PON, XG-PON andRF video overlay downstream signals, whereas the second extracteddownstream light portion 88 b is used to detect PtP NG-PON2 downstreamsignals.

In FIG. 3, the downstream filter assembly 18 includes a downstreamdemultiplexing assembly 90 that receives the first extracted downstreamlight portion 88 a from the downstream optical power splitter assembly86. The downstream demultiplexing assembly 90 is configured tospectrally split the first extracted downstream light portion 88 a intoa plurality of downstream spectral bands, namely four downstreamspectral bands in the illustrated embodiment. More particularly, thefour downstream spectral bands include:

-   -   a first downstream spectral band ranging from 1575 nm to 1580        nm, which corresponds to XG-PON downstream signals associated        with upstream signals in the first upstream spectral band (1260        nm to 1280 nm);    -   a second downstream spectral band ranging from 1480 nm to 1500        nm, which corresponds to ABG-PON downstream signals associated        with upstream signals in the second upstream spectral band (1290        nm to 1330 nm);    -   a third downstream spectral band ranging from 1550 nm to 1560        nm, which corresponds to downstream video signals associated        with upstream signals also in the second upstream spectral band        (1290 nm to 1330 nm); and    -   a fourth downstream spectral band ranging from 1596 nm to 1603        nm, which corresponds to TWDM NG-PON2 downstream signals        associated with upstream signals in the third upstream spectral        band (1524 nm to 1544 nm).

By way of example, the downstream filter assembly 18 may include threecascaded wavelength demultiplexers based, for instance, onwavelength-dependent fused couplers or bulk filters. Of course, otherembodiments may use different configurations for the downstream filterassembly 18.

As mentioned above, when the second network element 26 is a NG-PON2device, the processing unit 16 is configured to determine not only thedownstream spectral band in which to find the downstream signal ofinterest, but also a central wavelength value of the downstream signalof interest. The processing unit 16 can determine the expected value ofthe central wavelength of the downstream signal of interest from themeasured value of the central wavelength of the upstream light (asmeasured by the third upstream detection circuit 72 c in FIG. 3) byconsulting reference data (e.g., a prerecorded lookup table) relating aset of possible central wavelength values for the upstream light to aset of possible central wavelength values for the downstream signal ofinterest.

In the case of a TWDM NG-PON2 mode of operation, several downstreamsignals in different WDM downstream wavelength channels reach the secondnetwork element 26, although only one downstream signal is actuallyread. To account for this mode of operation, the downstream filterassembly 18 can be provided with a tunable bandpass optical filter 94configured to receive filtered light from the downstream demultiplexingassembly 90 in the fourth downstream spectral band (1596 nm to 1603 nm;TWDM NG-PON2 transmission). The tunable bandpass optical filter 94 has apassband central wavelength that can be adjusted to the value of thecentral wavelength of the downstream signal of interest determined bythe processing unit 16. It will be understood that the provision of thetunable bandpass optical filter 94 enables the selection of the relevantdownstream wavelength channel in the fourth downstream spectral band,and the subsequent measure of its optical power (see below). Inparticular, the passband central wavelength of the filter 94 can beautomatically adjusted directly or indirectly by the processing unit 16as a function of the measured central wavelength value of the upstreamlight 32.

Meanwhile, the second extracted downstream light portion 88 b is sentdirectly to the downstream optical power meter assembly 20.

In the illustrated embodiment, the downstream optical power meterassembly 20 includes a plurality of power meter devices 92 a to 92 e.Each power meter device 92 a to 92 e is configured to measure an opticalpower parameter of a corresponding signal received from the downstreamfilter assembly 18. However, only one of the optical power parametersmeasured by the plurality of power meter devices 92 a to 92 ecorresponds to the “optical power parameter of interest”, that is, theoptical power parameter associated with the extracted portion of thedownstream signal of interest. As mentioned above, the processing unit16 can determine which of the plurality of power meter devices 92 a to92 e measures the optical power parameter of interest based on thedetermination of the downstream spectral characteristic (e.g., centralwavelength or presence in a certain wavelength range) of the downstreamsignal of interest from the measured upstream spectral characteristic ofthe upstream light.

In some implementations, the downstream optical power meter assembly canbe configured to measure only one optical power parameter, namely theoptical power parameter of the downstream signal of interest asdetermined by the processing unit. In some of these implementations, theprocessing unit may be configured to instruct the downstream opticalpower meter assembly to make optical power measurements only with thepower meter device that receives the downstream signal of interest. Inother of these implementations, the downstream optical power meterassembly can include a single power meter device and a selector, theselector being configured to select, based on the determination made bythe processing unit, the downstream signal of interest among theplurality of downstream signals, and to direct the downstream signal ofinterest to the single power meter device for measurement of its opticalpower.

The first, second and third power meter devices 92 a, 92 b, 92 c receivefiltered light from the downstream demultiplexing assembly 90 in thefirst downstream spectral band (1575 nm to 1580 nm; XG-PONtransmission), the second downstream spectral band (1480 nm to 1500 nm;ABG-PON), and the third downstream spectral band (1550 nm to 1560 nm; RFvideo overlay transmission), respectively. Similarly, the fourth powermeter device 92 d receives filtered light outputted by the downstreamdemultiplexing assembly 90 in the fourth downstream spectral band (1596nm to 1603 nm; TWDM NG-PON2 transmission) and subsequently filteredfurther by the tunable bandpass optical filter 94.

In the illustrated embodiment of FIG. 3, each of the first, second,third and fourth power meter devices 92 a to 92 d includes an O/Econverter 74 (e.g., an InGaAs detector) for generating an electronicsignal representative of the detected filtered light from the downstreamdemultiplexing assembly 90, a transimpedance amplifier 76 for amplifyingthe electronic signal, and an ADC 80 for converting the amplifiedelectronic signal into digital output data. The digital output data isprocessed to yield a value that determines the optical power parameterof the extracted downstream light 50 in each of the first, second, thirdand fourth downstream spectral bands.

The fifth power meter device 92 e receives the second extracteddownstream light portion 88 b from the downstream optical power splitter86 in order to detect PtP NG-PON2 downstream signals in the range from1524 nm to 1625 nm. As known in the art, in the case of a PtP NG-PON2mode of operation, a single downstream signal at a single wavelengthreaches the second network element 26. The fifth power meter device 92 eis configured to measure not only the optical power of the secondextracted downstream light portion 88 b, but also its wavelength.Accordingly, the fifth power meter device 92 e can act as both asingle-wavelength meter and a power meter.

In the illustrated embodiment, the fifth power meter device 92 e in FIG.3 includes a bandpass splitting filter 96 that splits and filters thesecond extracted downstream light portion 88 b into first and secondsignals using a known or precalibrated wavelength-dependent splittingratio in a passband ranging from 1524 nm to 1625 nm. As for the bandpasssplitting filter 84 in the third upstream detection circuit 72 c, thebandpass splitting filter 96 can be embodied by a slope filter with thedesired or required passband.

The fifth power meter device 92 e also includes O/E converters 74 (e.g.,InGaAs detectors) for generating electronic signals representative ofthe two split signals, transimpedance amplifiers 76 for amplifying thetwo electronic signals, and an ADC 80 for converting the amplifiedelectronic signals into digital output data. The digital output data isprocessed to yield two power values. The sum of these two power valuesdetermines the optical power parameter associated with the secondextracted downstream light portion 88 b, whereas the ratio of these twopower values can be used to determine its wavelength, for example usinga prerecorded calibration table. The measured wavelength determines thededicated wavelength channel of the downstream signal. This informationmay be employed by the device 10 to verify that the downstream channelwavelength matches the measured upstream channel wavelength, thusproviding a useful troubleshooting feature. The value of measureddownstream wavelength may also be used to determine the propercalibration constant for the device 10.

It is to be noted that, in the illustrated embodiment, the fifth powermeter device 92 e will generally yield meaningful wavelength and opticalpower measurements only in the case of a PtP NG-PON2 operation where thedownstream light 30 includes a single downstream signal in the rangefrom 1524 nm to 1625 nm.

It is to be noted that the configurations for the plurality of powermeter devices 92 a to 92 e depicted in FIG. 3 are provided by way ofexample only, and may be varied in other implementations.

Likewise, the number and spectral ranges of the upstream and downstreamspectral bands considered in the exemplary embodiment of FIG. 3 are alsoexemplary only, and may be different in other embodiments. In thisregard, it is to be noted that some implementations of the devicedisclosed herein are intended to be modular in that the number and/orthe width of the downstream and upstream spectral bands covered by thedevice can be modified as required or desired by the particularapplication so that users are free to use as many or as few as necessaryto achieve adequate optical power testing. In particular, depending uponthe particular combination of PON standards used in a given customer'snetwork, only part of the configuration exemplified in FIG. 3 may beneeded. In such a case, it may be possible to reduce the cost of thedevice by including only those parts, configurations and functions thatare required given a priori knowledge about the hardware and topology ofthe network.

Third Embodiment of a Device for Optical Power Measurement

Referring now to FIG. 4, there is illustrated a third exemplaryembodiment of a device 10 operable as a PON power meter. Many featuresof this third embodiment can be generally similar to like featuresdescribed above for the first and second embodiments, and they will notbe described again in detail other than to highlight differences. Thethird embodiment of the device 10 generally includes an optical powersplitter assembly 12 configured to extract, from the opticaltransmission path 22, a portion 50 of the downstream light 30 and aportion 52 of the upstream light 32. The device 10 also includes anupstream wavelength analyzer 14, a processing unit 16, a downstreamfilter assembly 18, and a downstream optical power meter assembly 20.

The device 10 is suitable for optical power measurement along an opticaltransmission path 22 extending between a first network element 24 and asecond network element 26 in a multiple-wavelength PON 28. However, thePON 28 in FIG. 4 has a different architecture than that in the secondembodiment shown in FIG. 3, namely in that it supports coexistence ofNG-PON2 with ABG-PON, but not with XG-PON or RF video overlay.

In particular, the configuration of the upstream wavelength analyzer 14,the downstream filter assembly 18 and the downstream optical power meterassembly 20 is simpler in FIG. 4 than in FIG. 3. This is mostly due tothe fact that, as opposed to XG-PON and RF video overlay, the ABG-PONdownstream band (1480 nm to 1500 nm) does not overlap with the NG-PON2downstream channels (1524 nm to 1625 nm). This means that when theupstream light 32 is found in the spectral range from 1524 nm to 1625nm, it is expected to be confined to a single upstream wavelengthchannel characterized by a single central wavelength. As a result, theconfiguration of the upstream wavelength analyzer 14 in the embodimentof FIG. 4 can correspond to that of a single-wavelength meter, withoptional optical power measuring capabilities.

More particularly, the upstream wavelength analyzer 14 can be similar tothe third upstream detection circuit 72 of the embodiment of FIG. 3.Namely, the upstream wavelength analyzer 14 can include a bandpasssplitting filter 110 that splits and filters the extracted downstreamlight 50 from the optical power splitter assembly 12 into a first signal(signal A) and a second signal (signal B) with a known or precalibratedwavelength-dependent splitting ratio in a passband ranging from 1524 nmto 1625 nm, corresponding to the upstream spectral band for NG-PON2. Thebandpass splitting filter 110 may be embodied by a slope filter with thedesired or required passband. Of course, this configuration is providedby way of example only, and various other configurations ofsingle-wavelength meters can be used to implement the upstreamwavelength analyzer 14 depicted in FIG. 4.

The upstream wavelength analyzer 14 can also include O/E converters 74(e.g., InGaAs detectors) for generating electronic signalsrepresentative of signals A and B, and transimpedance amplifiers 76 foramplifying the two electronic signals. Each amplified electronic signalis sent to a respective peak-and-duration detector 82, where it is splitin two parts. Each first part is directed to a peak detector (P1A, P1B).Each second part is directed to a filter having a time constant longerthan the longest upstream burst to be detected by the device 10, andthen to a peak detector (P2A, P2B). An ADC 80 then converts the outputof the two peak-and-duration detectors 82 into digital output data.

The digital output data is processed to yield four power values. The sumof the power values corresponding to the two first parts (P1A+P1B)determines the optical power of the extracted upstream light 52, and theratio of the power values corresponding to two the second parts(P2A/P2B) is used to determine the central wavelength of the extractedupstream light 52 (and thus of the upstream light 32 itself), forexample using a prerecorded calibration table. Also, the ratio of thesum of the power values corresponding to the two first parts to the sumof the power values corresponding to the two second parts [i.e.,(P1A+P1B)/(P2A+P2B)] can be used to determine the upstream burstduration and, in turn, the upstream signal bitrate.

Once the value of the central wavelength of the upstream light 32 hasbeen determined by the upstream wavelength analyzer 14, the processingunit 16 can be used to determine the central wavelength of thedownstream signal of interest, for example by consulting NG-PON2reference data relating a set of possible central wavelength values forthe upstream light to a set of possible central wavelength values forthe downstream signal of interest. It will be understood that since thePON 28 in FIG. 4 supports only NG-PON2 and ABG-PON, it is not necessaryfor the upstream wavelength analyzer 14 to be configured for wavelengthmeasurements in the ABG-PON upstream band. Indeed, the processing unit16 will conclude that the upstream light 32 is an ABG-PON signalwhenever the upstream wavelength analyzer 14 does not detect a signal inthe NG-PON2 upstream band (i.e., from 1524 nm to 1625 nm).

Referring still to FIG. 4, the downstream filter assembly 18 receivesand spectrally filters the extracted downstream light 50 to selecttherefrom a portion of the downstream signal of interest according tothe determined downstream spectral characteristic. The downstream filterassembly 18 can include a downstream demultiplexing assembly 90configured to spectrally split the extracted downstream light 50 intotwo of downstream spectral bands, namely a first downstream spectralband ranging from 1524 nm to 1625 nm and corresponding to NG-PON2downstream signals (both TWDM and PtP), and a second downstream spectralband ranging from 1480 nm, or less, to 1500 nm and corresponding toABG-PON downstream signals.

More particularly, the downstream demultiplexing assembly 90 can includea tunable bandpass optical filter 94 configured to receive the extracteddownstream light 50. The tunable bandpass optical filter 94 can have apassband central wavelength tunable to the value of the centralwavelength of the downstream signal of interest determined by theprocessing unit 16 from the value of the upstream central wavelengthmeasured by the upstream wavelength analyzer 14. In the illustratedembodiment, the passband central wavelength of the bandpass opticalfilter 94 is tunable in a wavelength range extending from 1524 nm to1625 nm in order to encompass NG-PON2 signals. In some implementations,the passband central wavelength of the filter 94 can be automaticallyadjusted directly or indirectly by the processing unit 16 as a functionof the measured central wavelength value of the upstream light 32. Thedownstream demultiplexing assembly 90 can also include a second bandpassfilter 100 filtering light rejected by the tunable bandpass opticalfilter 94 in the second downstream spectral band (i.e., from 1480 nm to1500 nm) to select ABG-PON downstream signals.

Referring still to FIG. 4, the downstream optical power meter assembly20 includes a first power meter device 92 a configured to measure anoptical power parameter of the filtered output signal from the tunablebandpass filter 94, and a second power meter device 92 b configured tomeasure an optical power parameter of the filtered output signal fromthe second bandpass filter 100. Each of the first and second power meterdevices 92 a, 92 b can have a configuration similar to that of the powermeter devices 92 a to 92 e described above with reference to FIG. 3, oranother appropriate configuration.

As mentioned above, only one of two optical power parameters measured bythe first and the second power meter devices 92 a, 92 b corresponds tothe optical power parameter of interest, which can be determined by theprocessing unit 16. Namely, the processing unit 16 will determine thatthe optical power parameter of interest corresponds to that measured bythe first power meter device 92 a if the upstream wavelength analyzerdetects the presence of the upstream light 32 between 1524 nm and 1625nm, and to that measured by the second power meter device 92 b if theupstream wavelength analyzer does not detect the presence of theupstream light 32 between 1524 nm and 1625 nm.

Fourth Embodiment of a Device for Optical Power Measurement

Referring now to FIG. 5, there is illustrated a fourth exemplaryembodiment of a device 10 operable as a PON power meter. Again, manyfeatures of this fourth embodiment can be generally similar to likefeatures described above for the second embodiment with reference toFIG. 3. Accordingly, the fourth embodiment of the device 10 generallyincludes an optical power splitter assembly 12, an upstream wavelengthanalyzer 14, a processing unit 16, a downstream filter assembly 18, anda downstream optical power meter assembly 20. However, the fourthembodiment of the device 10 differs from the second embodiment mainly inthe configuration of the upstream wavelength analyzer 14. Moreparticularly the upstream wavelength analyzer 14 in FIG. 5 is configuredsuch that the measurement of the upstream spectral characteristic (e.g.,the wavelength or wavelength range) of the upstream light 32 isdecoupled from the measurement of its optical power. To this end, theupstream wavelength analyzer 14 includes an upstream optical powersplitter assembly 102, an upstream wavelength meter 104, and an upstreampower meter 106.

The upstream optical power splitter assembly 102 is configured toreceive the extracted upstream light 52 from the optical power splittingassembly 12, and to split it into respective first and second portions108 a, 108 b. In the illustrated embodiment, the upstream optical powersplitter assembly 102 has a 20:80 splitting ratio, but other splittingratio values can be used in other embodiments. The first portion 108 a(20%) is sent to the upstream wavelength meter 104, which is configuredto determine the upstream spectral characteristic (e.g., a wavelengthvalue or range) corresponding to the upstream light 32. Meanwhile, thesecond portion 108 b (80%) is sent to the upstream power meter 106,where its optical power is measured. The upstream power meter 106 canhave a configuration similar to that of the first and second upstreamdetection circuits 72 a, 72 b described above with reference to FIG. 3,or another appropriate configuration.

The processing unit 16 will use the wavelength information outputted bythe upstream wavelength meter 104 to determine the downstream spectralcharacteristic (e.g., a wavelength value or range) corresponding to thedownstream spectral of interest. The processing unit 16 will alsoidentify, based on the determined downstream spectral characteristic,the optical power parameter measured by the downstream optical powermeter assembly 20 corresponding to the optical power parameter of theportion of the downstream signal of interest. Furthermore, when theupstream light 32 corresponds to a NG-PON2 upstream signal, theprocessing unit 16 can be configured to tune a tunable passband centralwavelength of the downstream filter assembly 18 to the determined valueof the wavelength of the downstream signal of interest.

Fifth Embodiment of a Device for Optical Power Measurement

Referring now to FIG. 6, there is illustrated a fifth exemplaryembodiment of a device 10 operable as a PON power meter. The device 10of FIG. 6 is suitable for optical power measurement along an opticaltransmission path 22 extending between a first network element 24 and asecond network element 26 in a PON 28. In the illustrated embodiment,the first network element 24 is embodied by an OLT and the secondnetwork element 26 is embodied by an ONT. The optical transmission path22 supports concurrent, bidirectional propagation of downstream light 30and upstream light 32. The device 10 aims to measure the optical powerof a downstream signal of interest 38 in the downstream light 30.

This fifth embodiment shares many features with the embodimentspresented above, which will not be described again in detail other thanto highlight differences. The device 10 in FIG. 6 generally includes anoptical power splitter assembly 12 configured to extract, from theoptical transmission path 22, a portion 50 of the downstream light 30and a portion 52 of the upstream light 32. The device 10 also includesan upstream wavelength analyzer 14, a processing unit 16, a downstreamfilter assembly 18, and a downstream optical power meter assembly 20, asdescribed further below.

The PON 28 in FIG. 6 has a different architecture than those in FIGS. 2to 5, namely in that it supports coexistence of only two PON standardsor layers (excluding RF video overlay). The two coexisting PON standardshave non-spectrally-overlapping upstream transmission windows as well asnon-spectrally-overlapping downstream transmission windows. In someimplementations, one of the two PON standards can be ABG-PON (upstreamtransmission window: 1290 nm to 1330 nm; downstream transmission window:1480 nm to 1500 nm), and the other one can be a “newer” PON standard.For example, in the embodiment of FIG. 6, the other PON standard is TWDMNG-PON2 (upstream transmission window: 1524 nm to 1544 nm; downstreamtransmission window: 1596 nm to 1603 nm). However, in other embodiments,the other PON standard can be XG-PON (upstream transmission window: 1260nm to 1280 nm; downstream transmission window: 1575 nm to 1580 nm).Other possible configurations can include, without limitation, EPON and10G-EPON; GPON and XGS-PON; EPON and XG-PON; EPON and XGS-PON; EPON andNG-PON2; GPON and 10G-EPON; and the like. In FIG. 6, the PON 28 alsooptionally supports a downstream video overlay band (1550 nm to 1560 nm)which, however, may not be present in other embodiments. In a typicaloperation, the user can enter a configuration file in which he or sheprovides information about the PON layers present in the PON 28 undertest. Then, the processing unit 16 can detect the appropriate modulationformat from those given in the configuration file to adjust the opticalcalibration of the detectors as well as the pass/fail thresholdsassociated with the PON standards supported in the PON 28 under test.

The upstream wavelength analyzer 14 is configured to receive theextracted portion 52 of the upstream light 32 from the optical powersplitter assembly 12, and to determine therefrom an upstream spectralcharacteristic of the upstream light 32. In FIG. 6, the upstreamspectral characteristic corresponds to the presence of the upstreamlight 32 in either the ABG-PON upstream spectral band or the NG-PON2upstream spectral band. It is to be noted that unlike previouslydescribed embodiments, the embodiment of FIG. 6 is configured forsingle-wavelength NG-PON2 implementation, in which a single upstreamwavelength channel and a single downstream wavelength channel are used.In such a case, the specific upstream and downstream wavelengths beingused in the NG-PON2 layer of the PON under test need not be determinedby the device of FIG. 6. Of course, in other applications, theembodiment of FIG. 6 could be adapted for multiple-wavelength NG-PON2operation, for example using the principles described above.

In FIG. 6, the upstream wavelength analyzer 14 generally includes anupstream optical power splitter assembly 102, an upstream filterassembly 66, and an upstream detection assembly 70 having first andsecond upstream detection circuits 72 a, 72 b. The upstream opticalpower splitter assembly 102 is configured to receive the extractedupstream light 52 from the optical power splitting assembly 12, and tosplit it into a first upstream light component 114 a and a secondupstream light component 114 b. The upstream optical power splitterassembly 102 typically has a 50:50 splitting ratio, but other splittingratio values can be used in other embodiments.

The first upstream light component 114 a of the extracted upstream light52 is sent directly, as an unfiltered upstream signal, to the firstupstream detection circuit 72 a of the upstream detection assembly 70.The first upstream detection circuit 72 a is configured to measure anoptical power parameter P₁ associated with the first upstream lightcomponent 114 a of the extracted upstream light 52. The first upstreamdetection circuit 72 a can have a configuration corresponding to thoseof the detection circuits described above, or another suitableconfiguration.

The second upstream light component 114 b of the extracted upstreamlight 52 is sent to the upstream filter assembly 66, which outputs afiltered upstream signal 116. The upstream filter assembly 66 includesan upstream bandpass filter configured to allow passage of light in anupstream spectral band encompassing the upstream transmission window ofone of the two coexisting PON layers in the PON 28. In FIG. 6, thepassband of the upstream bandpass filter is centered on 1310 nm. Thispassband central wavelength corresponds to the central wavelength of theupstream transmission window of ABG-PON, which extends from 1290 to 1330nm. Preferably, the upstream passband filter has high out-of-band signalrejection or attenuation to enhance performance, for example 10 dB ormore.

The filtered signal 116 outputted by the upstream filter assembly 66 issent to the second upstream detection circuit 72 b of the upstreamdetection assembly 70. The second upstream detection circuit 72 b isconfigured to measure an optical power parameter P₂ associated with thefiltered upstream signal 116. The optical power parameter P₂ ispreferably of the same nature or measured in the same manner as theoptical power parameters P₁ of the first upstream light component 114 aof the extracted upstream light 52, to allow straightforward comparisonbetween P₁ and P₂. Like the first upstream detection circuit 72 a, thesecond upstream detection circuit 72 b can have a configurationcorresponding to those of the detection circuits described above, oranother configuration.

Referring still to FIG. 6, the optical power parameters P₁ and P₂ can becompared or otherwise used to yield a detection signal indicative of theupstream spectral characteristic of the upstream light 32 and conveyinginformation about a presence of the upstream light 32 in one of thefirst and second upstream transmission bands. For example, where theupstream optical power splitter assembly 102 has a 50:50 splittingratio, P₁ and P₂ are expected to be nearly identical, or at leastsubstantially similar, when the upstream light 32 is an ABG-PON signal,whose spectrum is contained in the passband of the upstream filterassembly 66. In contrast, P₁ and P₂ are expected to be significantlydifferent from each other (e.g., P₁>>P₂) when the upstream light is anNG-PON2 signal, whose spectrum lies well outside the passband of theupstream filter assembly 66. In some implementations, the detectionsignal indicative of the upstream spectral characteristic can be basedon a ratio between P₁ and P₂. Then, depending on the value of this ratiorelative to a certain threshold value, the detection signal will conveyinformation about whether the upstream light 32 is an ABG-PON signal oran NG-PON2 signal.

The upstream detection assembly 70 is coupled to the processing unit 16.The processing unit 16 is configured to receive, from the upstreamdetection assembly 70, the detection signal indicative of the upstreamspectral characteristic and to determine therefrom a downstream spectralcharacteristic of the downstream signal of interest 38 in the downstreamlight 30. For example, in the embodiment of FIG. 6, the downstreamspectral characteristic is a spectral range in which the downstreamsignal of interest 38 is expected to lie. More particularly, thisspectral range is the NG-PON2 downstream band (1596 nm to 1603 nm) ifthe upstream light is an NG-PON2 signal, and the ABG-PON downstream band(1480 nm to 1500 nm) if the upstream light is an ABG-PON signal. Otherdownstream spectral ranges can be used in other embodiments,corresponding to other network standards.

Referring still to FIG. 6, the downstream filter assembly 18 receivesand spectrally filters the extracted downstream light 50 to selecttherefrom a portion of the downstream signal of interest 38 according tothe determined downstream spectral characteristic. The downstream filterassembly 18 can include a downstream demultiplexing assembly 90configured to spectrally split the extracted downstream light 50 intothree downstream spectral bands. The downstream filter assembly 18 mayinclude cascaded wavelength demultiplexers, although various othersplitting and filtering configurations and arrangements may also beused. In FIG. 6, the three downstream spectral bands are as follows:

-   -   a first downstream spectral band ranging from 1575 nm to at        least 1603 nm and encompassing NG-PON2 downstream signals        associated with NG-PON2 upstream signals rejected by the        upstream filter assembly 66 (i.e., between 1524 nm to 1544 nm);    -   a second downstream spectral band ranging from 1480 nm to 1500        nm and encompassing ABG-PON downstream signals associated with        ABG-PON upstream signals passed by the upstream filter assembly        66; and    -   a third downstream spectral band ranging from 1550 nm to 1560 nm        and encompassing downstream video signals.

It is to be noted that when the lower end of the first downstreamspectral band is equal to 1575 nm, the embodiment of FIG. 6 can also beused directly in implementations where the PON layers in the PON 28under test are ABG-PON and XG-PON rather than ABG-PON and NG-PON2, sincethe XG-PON downstream signals lie in a spectral band ranging from 1575nm to 1580 nm.

Referring still to FIG. 6, the downstream optical power meter assembly20 includes three power meter devices 92 a to 92 c coupled to thedownstream filter assembly 18. Each one of the power meter devices 92 ato 92 c measures an optical power parameter of the filtered lightoutputted by the downstream demultiplexing assembly 90 in thecorresponding one of the three downstream spectral bands. Depending onthe application, the power meter devices 92 a to 92 c depicted in FIG. 6may be implemented as described in previous embodiments, or may haveother suitable configurations. As mentioned above, only one of theoptical power parameters measured by the three power meter devices 92 ato 92 c corresponds to the “optical power parameter of interest”, thatis, the optical power parameter associated with the extracted portion ofthe downstream signal 38 of interest. As also mentioned above, theprocessing unit 16 can determine which of the power meter devices 92 ato 92 c measures the optical power parameter of interest based on thedetermination of the downstream spectral characteristic (e.g., presencein a certain downstream spectral range) of the downstream signal ofinterest from the measured upstream spectral characteristic (e.g.,presence in a certain upstream spectral range) of the upstream light.

Method for Optical Power Measurement

Referring to FIG. 7, there is provided a flow chart of an embodiment ofa method 200 for optical power measurement along an optical transmissionpath between a first network element and a second network element. Theoptical transmission path supports bidirectional propagation ofdownstream light and upstream light, the downstream light including aplurality of downstream signals having mutually different centralwavelengths. The method 200 can be performed using a device such asdescribed above with reference to FIGS. 2 to 6, or another device.

Broadly described, the implementation of the method 200 depicted in FIG.7 involves a step 202 of extracting, from the optical transmission path,a portion of the downstream light and a portion of the upstream light.The method 200 also includes a step 204 of determining, from theextracted portion of the upstream light, an upstream spectralcharacteristic of the upstream light, followed by a step 206 ofdetermining, based on the upstream spectral characteristic, a downstreamspectral characteristic of a downstream signal of interest among theplurality of downstream signals. The method 200 further includes a step208 of filtering the extracted portion of the downstream light to selecttherefrom a portion of the downstream signal of interest according tothe determined downstream spectral characteristic, followed by a step210 of measuring an optical power parameter of the selected portion ofthe downstream signal of interest.

In some implementations, the step 204 determining the upstream spectralcharacteristic can include measuring a value of a central wavelength ofthe upstream light, and the step 206 of determining the downstreamspectral characteristic can include determining a value of a centralwavelength of the downstream signal of interest. In suchimplementations, the determination of the value of the centralwavelength of the downstream signal of interest can include accessingreference data relating a set of possible central wavelength values forthe upstream light to a set of possible central wavelength values forthe downstream signal of interest.

In some implementations, the step 208 of filtering the extracted portionof the downstream light can include tuning a passband center wavelengthto the determined value of the central wavelength of the downstreamsignal of interest, for example in a wavelength range extending from1524 nm to 1625 nm, or from 1596 nm to 1603 nm.

In some implementations, the step 204 of determining the upstreamspectral characteristic can include monitoring a presence of theupstream light in each of a plurality of distinct upstream spectralbands and, upon detection of the presence of the upstream light in oneof the upstream spectral bands, generating a detection signal indicativeof the upstream spectral characteristic.

In some implementations, the step 208 of filtering the extracted portionof the downstream light can include spectrally splitting the extractedportion of the downstream light into a plurality of downstream spectralbands. In such implementations, the step 210 of measuring the opticalpower parameter of the portion of the downstream signal of interestincludes measuring an optical power parameter of a filtered signal ineach of the downstream spectral bands, such that one of the opticalpower parameters measured by the power meter devices corresponds to theoptical power parameter of the portion of the downstream signal ofinterest.

In some implementations, the method 200 further includes identifying,based on the determined downstream spectral characteristic, the one ofthe optical power parameters measured by the power meter devicescorresponding to the optical power parameter of the portion of thedownstream signal of interest.

Of course, various modifications could be made to the embodimentsdisclosed herein and still be within the scope of the following claims.

1. A device for optical power measurement in an optical networksupporting upstream and downstream signal propagation along an opticaltransmission path, the device comprising: an upstream wavelengthanalyzer receiving upstream light extracted from the opticaltransmission path and configured to determine an upstream spectralcharacteristic of the extracted upstream light; a downstream filterassembly receiving downstream light extracted from the opticaltransmission path and configured to spectrally split the extracteddownstream light into a plurality of downstream filtered signals, one ofwhich corresponding to a downstream signal of interest; a processingunit configured to identify, based on the upstream spectralcharacteristic, the downstream signal of interest among the plurality ofdownstream filtered signals; and a downstream optical power meterassembly coupled to the downstream filter assembly and configured tomeasure an optical power parameter of the downstream signal of interest.2. The device of claim 1, wherein the upstream wavelength analyzer isconfigured to output the upstream spectral characteristic as a detectionsignal corresponding to a wavelength value of the extracted upstreamlight.
 3. The device of claim 1, wherein the upstream wavelengthanalyzer is configured to output the upstream spectral characteristic asa detection signal conveying information about a presence of theextracted upstream light in a specific upstream spectral range.
 4. Thedevice of claim 3, wherein the specific upstream spectral rangecorresponds to one among a first upstream spectral band ranging fromabout 1260 nm to 1280 nm, a second upstream spectral band ranging fromabout 1290 nm to about 1330 nm, and a third upstream spectral bandranging from about 1524 nm to about 1544 nm.
 5. The device of claim 1,wherein the processing unit is configured to identify the downstreamsignal of interest among the plurality of downstream filtered signals bydetermining an expected value of a spectral position of the downstreamsignal of interest.
 6. The device of claim 1, wherein the processingunit is configured to identify the downstream signal of interest amongthe plurality of downstream filtered signals by determining an expecteddownstream spectral range in which to find the downstream signal ofinterest.
 7. The device of claim 6, wherein the expected downstreamspectral range corresponds to one among a first downstream spectral bandranging at least from 1575 nm to about 1580 nm, a second downstreamspectral band ranging from about 1480 nm to about 1500 nm, a thirddownstream spectral band ranging from about 1550 nm to about 1560 nm,and a fourth downstream spectral band ranging from about 1596 nm toabout 1603 nm.
 8. The device of claim 1, wherein the optical networksupports coexistence of at least a first network standard and a secondnetwork standard, the first and second network standards havingspectrally distinct first and second upstream transmission bands, andwherein the upstream wavelength analyzer comprises: an upstream opticalpower splitter assembly configured to split the extracted upstream lightinto a first upstream light component and a second upstream lightcomponent; an upstream filter assembly configured to filter, as afiltered upstream signal, the second upstream light component in apassband containing only one of the first and second upstreamtransmission bands; and an upstream detection assembly configured tomeasure a first optical power parameter of the first upstream lightcomponent and a second upstream optical power parameter of the filteredupstream signal, the upstream detection assembly generating a detectionsignal based on the first and second optical power parameters, thedetection signal being indicative of the upstream spectralcharacteristic and conveying information about a presence of theupstream light in one of the first and second upstream transmissionbands.
 9. The device of claim 8, wherein the first upstream transmissionband ranges from about 1524 nm to about 1544 nm and the second upstreamtransmission band ranges from about 1290 nm to about 1330 nm.
 10. Thedevice of claim 9, wherein, when the extracted upstream light is foundto be present in the first upstream transmission band, the processingunit determines that the downstream signal of interest lies in a firstdownstream transmission band ranging from about 1596 nm to about 1603nm, and wherein, when the extracted upstream light is found to bepresent in the second upstream transmission band, the processing unitdetermines that the downstream signal of interest lies in a seconddownstream transmission band ranging from about 1480 nm to about 1500nm.
 11. The device of claim 8, wherein the first upstream transmissionband ranges from about 1260 nm to about 1280 nm and the second upstreamtransmission band ranges from about 1290 nm to about 1330 nm.
 12. Thedevice of claim 11, wherein, when the extracted upstream light is foundto be present in the first upstream transmission band, the processingunit determines that the downstream signal of interest lies in a firstdownstream transmission band ranging from about 1575 nm to about 1580nm, and wherein, when the extracted upstream light is found to bepresent in the second upstream transmission band, the processing unitdetermines that the downstream signal of interest lies in a seconddownstream transmission band ranging from about 1480 nm to about 1500nm.
 13. The device of claim 1, wherein the optical network supportscoexistence of at least a first network standard and a second networkstandard, the first network standard having a first upstreamtransmission band ranging from about 1524 nm to about 1544 nm and thesecond network standard having a second upstream transmission bandranging from about 1290 nm to about 1330 nm, wherein, when the extractedupstream light is found to be present in the first upstream transmissionband, the processing unit determines that the downstream signal ofinterest lies in a first downstream transmission band ranging from about1596 nm to about 1603 nm, and wherein, when the extracted upstream lightis found to be present in the second upstream transmission band, theprocessing unit determines that the downstream signal of interest liesin a second downstream transmission band ranging from about 1480 nm toabout 1500 nm.
 14. A method for optical power measurement in an opticalnetwork supporting upstream and downstream signal propagation along anoptical transmission path, the method comprising: receiving upstreamlight extracted from the optical transmission path; determining anupstream spectral characteristic of the extracted upstream light;receiving downstream light extracted from the optical transmission path;spectrally splitting the extracted downstream light into a plurality ofdownstream filtered signals, one of which constituting a downstreamsignal of interest; identifying, based on the upstream spectralcharacteristic, the downstream signal of interest among the plurality ofdownstream filtered signals; and measuring an optical power parameter ofthe downstream signal of interest.
 15. The method of claim 14, whereindetermining the upstream spectral characteristic comprises generating adetection signal corresponding to a wavelength value of the extractedupstream light.
 16. The method of claim 14, wherein determining theupstream spectral characteristic comprises generating a detection signalconveying information about a presence of the extracted upstream lightin a specific upstream spectral range.
 17. The method of claim 14,wherein identifying the downstream signal of interest among theplurality of downstream filtered signals comprises determining anexpected value of a spectral position of the downstream signal ofinterest.
 18. The method of claim 14, wherein identifying the downstreamsignal of interest among the plurality of downstream filtered signalscomprises determining an expected downstream spectral range in which tofind the downstream signal of interest.
 19. The method of claim 14,wherein the optical network supports coexistence of at least a firstnetwork standard and a second network standard, the first and secondnetwork standards having spectrally distinct first and second upstreamtransmission bands, the method further comprising: splitting theextracted upstream light into a first upstream light component and asecond upstream light component; filtering, as a filtered upstreamsignal, the second upstream light component in a passband containingonly one of the first and second upstream transmission bands; measuringa first optical power parameter of the first upstream light componentand a second upstream optical power parameter of the filtered upstreamsignal; and generating a detection signal based on the first and secondoptical power parameters, the detection signal being indicative of theupstream spectral characteristic and conveying information about apresence of the upstream light in one of the first and second upstreamtransmission bands.
 20. The method of claim 19, wherein the firstupstream transmission band ranges from about 1524 nm to about 1544 nm,and the second upstream transmission band ranges from about 1290 nm toabout 1330 nm, the method further comprising: determining that thedownstream signal of interest lies in a first downstream transmissionband ranging from about 1596 nm to about 1603 nm when the extractedupstream light is found to be present in the first upstream transmissionband; and determining that the downstream signal of interest lies in asecond downstream transmission band ranging from about 1480 nm to about1500 nm when the extracted upstream light is found to be present in thesecond upstream transmission band.
 21. The method of claim 19, whereinthe first upstream transmission band ranges from about 1260 nm to about1280 nm, and the second upstream transmission band ranges from about1290 nm to about 1330 nm, the method further comprising: determiningthat the downstream signal of interest lies in a first downstreamtransmission band ranging from about 1575 nm to about 1580 nm when theextracted upstream light is found to be present in the first upstreamtransmission band; and determining that the downstream signal ofinterest lies in a second downstream transmission band ranging fromabout 1480 nm to about 1500 nm when the extracted upstream light isfound to be present in the second upstream transmission band.
 22. Themethod of claim 14, wherein the optical network supports coexistence ofat least a first network standard and a second network standard, thefirst network standard having a first upstream transmission band rangingfrom about 1524 nm to about 1544 nm and the second network standardhaving a second upstream transmission band ranging from about 1290 nm toabout 1330 nm, the method further comprising: determining that thedownstream signal of interest lies in a first downstream transmissionband ranging from about 1596 nm to about 1603 nm when the extractedupstream light is found to be present in the first upstream transmissionband; and determining that the downstream signal of interest lies in asecond downstream transmission band ranging from about 1480 nm to about1500 nm when the extracted upstream light is found to be present in thesecond upstream transmission band.